Turbochargers may improve the performance of internal combustion engines by delivering a greater mass of air to the combustion process, relative to a naturally aspirated engine, thereby allowing a greater amount of fuel to be burned during each combustion cycle and realizing an associated power increase. A turbine wheel is driven by exhaust gasses from the combustion process, and in turn drives a compressor that compresses ambient air and delivers the compressed charge of air to the engine intake to be mixed with fuel for the combustion process.
The pressure of the compressed charge of air delivered to the engine intake must be controlled to prevent over-pressurizing the engine intake, which may lead to engine damage and/or decreased engine performance. A variety of mechanisms and arrangements are commonly used for controlling the pressure of the intake charge. For example, the engine intake may include a blow-off valve which may release excess pressure from the intake manifold. On the exhaust side of the engine, a wastegate may be employed to allow at least a portion of the exhaust gasses from the engine to bypass the turbine, thereby controlling the rotational speed of the turbine and the attendant compression of the intake charge by the compressor.
A wastegate may include a mechanical valve which may be operated based on one or more of the turbine rotational speed, intake pressure, engine performance, intake mass air flow, etc. The mechanical valve of the wastegate may be actuated by a mechanical or an electromechanical actuator. Conveniently, a pressure or a vacuum actuator may be used to control the wastegate. Such valves rely on a vacuum source or pressurized air acting against a diaphragm, e.g., working against a spring, to open and close the wastegate.
The vacuum or pressure supplied to the wastegate actuator may be controlled by, for example, a boost controller. The boost controller may include a solenoid valve, which may be controlled based on any of the foregoing parameters, to operate the wastegate to control the turbocharger boost pressure. In particular, the boost controller may be configured to control the boost level produced in the intake manifold of the engine by affecting the air pressure delivered to the wastegate. Some turbocharger systems include an electronic boost control system, wherein the solenoid valve is controlled by an electronic control unit (ECU) and the system may utilize pulse width modulation (PWM) techniques when controlling the vacuum or pressure supplied to the wastegate.